Elongated structures for use with vehicles, such as airplanes, are available in a wide variety of configurations to provide structural support under a variety of loading conditions. In particular, the wing and fuselage surfaces of an aircraft typically include parallel and span-wise oriented structural members called stringers. Such stringers are typically operably coupled to skin members on the wing and fuselage surfaces that cooperatively provide the desired flexural and torsional stiffness to the wing and fuselage surfaces. Such wing and fuselage surfaces may be fabricated from a metal materials, such as aluminum, steel or titanium or non-metal materials. The stringer may include a planar web portion that is generally oriented in a direction approximately perpendicular to the skin member and extending in a span wise direction along the wing or fuselage surface so that the web portion offers resistance to a bending moment generated by the load.
A flange portion may be positioned on one or both of the longitudinal edges of the web portion in order to provide resistance to localized failure of the web portion due to lateral buckling. The flange portion further allows the stringer to be coupled to the skin member and/or frame members by providing an attachment surface for the skin member. The stringer also may help carry and/or transfer loads. For example, a stringer may transfer a load from a skin panel to another structure. This other structure may be, for example, a frame or rib.
Although such elongated structures can offer certain superior bending stiffness properties over other design configurations, one issue that may tend to limit the usage of certain elongated structures is the difficulty of attaching the elongated structure to adjacent structures with adequate load transfer at the attachment region without undue increase in weight and cost. For example, typically attachment fittings must be machined in order to facilitate the proper attachment of certain elongated structures to various types of related structures, such as wing or fuselage frame members. While in certain situations it can be relatively easy to attach certain elongated structures when the applied loads are low, it is quite a challenge to do so for highly loaded structure.
Designing stringers with a desired weight and performance characteristics may also be challenging. For example, a stringer with desired performance characteristics may be more structural and geometrically complex or may weigh more than desired. With increased structural and geometrical complexity, time and cost for manufacturing a stringer also may increase. If the stringer has a desired weight, performance characteristics may be such that additional stringers may be required where a single stringer is desired. Therefore, it would be advantageous to have a method and apparatus that takes into account at least some of the issues discussed above, as well as possibly other issues.
Although desirable results have been achieved using prior art apparatus and methods, a stringer and skin structure that may be more easily and inexpensively fabricated, and that may provide a more favorable strength to weight ratio in comparison to certain known stringer and skin structures, would have utility.
There is, therefore, a need for a more cost effective and less labor intensive method of assembling elongated structures and their related assemblies. It would also be desirable to reduce or eliminate the need for the total number of stringers for certain aircraft assemblies (i.e., the fuselage and wings) in order to reduce the overall weight and assembly time. It would also be desirable to reduce the number of stingers required to attach the skin to the stringers and the frame. It would also be desirable to be able to tailor or vary an elongated structure's geometry so as to be able to adequately withstand different types or varying types of loads that the elongated structure will undergo along the length of the elongated structure, so as to minimize the amount of structure material and therefore weight of the elongated structure. Such a desired cost effective and less labor intensive assembled structures should also offer a more efficient method of providing a more robust attachment of stringers to frame members while also increasing manufacturing facility throughput while also driving down overall system manufacturing costs.